Stackable filter device

Details Stackable filter device Stackable filter device

1999-11-22

2002-10-22

Lewis, Aaron J. (Department: 3737)

Surgery

Respiratory method or device

Means for removing substance from respiratory gas

C128S205270, C128S205290

Reexamination Certificate

active

06467481

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to the field of air filter devices. More particularly, filter devices structured for coupling with a breathing apparatus, such as a respirator or mask or other source of suction, and so as to provide multiple filter elements functioning as a single filtering unit.
2. Description of the Related Art
When a person is subject to adverse breathing conditions, such as in an environment contaminated with airborne particles and/or harmful vapors, that person's safety and health will require some type of device for filtering the air before it passes into his or her lungs. To achieve this goal, requirements for such filtering devices have been codified (42 C.F.R. §84) by the National Institute of Occupational Safety and Health (NIOSH). NIOSH regulations were revised to be made substantially more stringent (in June 1995, with a grandfather clause for three years, effective June 1998), to require that these filtering devices demonstrate increased efficiency, a measure of its ability to remove contaminants from air as it is drawn (breathed) through the filtering device.
Historically, improvements in the efficiency of a filtering device have resulted in a concomitant increase in the difference in air pressure between the environment and the interior of the filtering device required for drawing air through it at a given rate. This pressure differential is commonly referred to as pressure drop of the filtering device. Further, increased efficiency in a filtering device also typically has led to a reduction in the effective life span of the filtering device. Consequently, with prior art filtering devices, greater safety through improved filter efficiency has typically made such devices difficult to breathe through and of extremely limited life span. As a result, in addition to breathing discomforts, users experience frequent periods of down time as they must either leave the work area and/or stop working to remove and replace filtering devices.
Accordingly, it has long been a goal of those in the field of filtering devices to develop a filtering device that meets the natural and codified safety requirements of users while demonstrating a pressure drop that is sufficiently low to allow comfortable breathing by the user and, even more importantly, while A functioning effectively for a greater period of time.
To attain such improvements, inventors have manipulated the shapes and sizes of the air filters to maximize surface area in the hope that, with increased area over which filtering can be conducted, acceptable efficiency can be realized while at the same time affording the user a low pressure drop and, thus, comfortable breathing. However, filters can be made only so large before they begin to interfere with a user's vision or mobility. Inventors have also experimented with improved materials in attempted furtherance of the same goals. To date, even slight improvements in efficiency, pressure drop, or life span have been hailed as marked improvements in the art.
One attempt to increase the surface area of the filter is illustrated in U.S. Pat. No. 2,130,555 to Malcolm. The Malcolm patent shows a dust filter unit of a generally tubular form, but having within the unit a filter having a plurality of bellows-like folds. The bellows-like folds provide increased surface area in the filter without the necessity of increasing the diameter of the unit.
The filter unit shown by Malcolm has the advantage of increasing the surface area of the filter medium. However, the folds are part of an integrally formed filter media. Therefore, the design does not permit more or less surface area to be used in accordance with particular needs.
U.S. Pat. No. 2,227,959 to Cover shows a filter composed of three elements connected to one another. The three elements are each structured differently from one another so as to be placed at an assigned position in the filter. However, the device requires specialized innermost and outermost filter elements, which would require that at least three types of filter units be kept in stock at all times. Further the construction of the filter shown in Cover, in which the filter walls are tucked into a cavity in a retaining plate, would be somewhat prone to leakage, compared to modern units in which the filter walls are sealingly engaged to one another around their periphery, and might not meet the more stringent standards in effect today, such as those promulgated by NIOSH.
U.S. Pat. No. 2,235,624 to Schwartz shows a filter unit for respirators having a cylindrical filter casing of a depth sufficient to hold two disk-shaped filter pads. The filter pad within the casing farthest away from the breathing mask is formed of two circular pads stitched together circumferentially at the edges to form the disk-shaped filter pad, and having an aperture formed through both circular pads to allow a supporting tube element to pass there through. The disk-shaped filter pad closest to the mask is formed similarly but is only apertured on one side. The supporting tube enters the aperture of this innermost pad and comes to an end therein without passing entirely through the innermost pad.
The filter unit taught by Schwartz has several disadvantages. For one thing, the requirement of rigidity of the outer cylindrical filter holder would tend to increase the weight of the mask. Also, since the depth of the filter holder is set, only a set number of the disk-shaped filter pads may be used. Moreover the innermost filter pad is of a different construction than the outermost pad, which means that, similar to the situation in the Cover patent, two types of replacement filter elements must be maintained in stock.
U.S. Pat. No. 2,951,551 to West shows an air purifying cannister that is formed from individual filtration units fitted together. Each unit has a male as well as a female connector and a rigid outer wall. The units may be mated in series ad infinitum to form a composite cannister of desired length. Each unit has a tube formed therethrough to allow for the passage of already-filtered air from one unit to the next. The tube is fitted with a cap on the unit farthest from the mask or source of suction to prevent unfiltered air from entering the tube.
The West filter unit, due to the requirement for rigidity, would become very heavy and would be very uncomfortable for the wearer after prolonged use, especially in comparison to the light-weight simple disk filter pad units currently preferred for long term use. Further the weight of the cannister, as additional units are added, would cause a great deal of stress to be applied to the air inlet of any mask using the filter, which may lead to fatigue of the connection materials and eventual breakage.
A common disadvantage of the types of filter units described above is the high ratio of non-functioning structural materials to functioning filtration material. As a result of this ratio, providing the user with increased filter surface area would result in an associated increase in weight of the filter. Modern filter units are expected to be light in weight, to ensure the comfort of the user.
A prevalent type of light-weight filter pad currently in use is the 3M® P100 Particulate filter, which consists of a single light-weight disk-shaped unit, formed of two fabric filter pads affixed to one another around the circumference of each pad. One of the filter pads has a central aperture being supported around its periphery by a plastic fastener integrally formed with a bayonet-style female connector, formed to enable a locking connection with a counterpart male connector at the input or inputs of a breathing mask.
However, while the 3M® P100 filter pad offers the advantage of light weight, due to its construction it can function only as a single unit. Further, because the pad is soft, installation and removal of the filter pad exerts torsional and crushing stress on the filter material as the user grips and twists the filter to engage or disengage the connector

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